As is said that except the food grown in your own garden, all food products have preservatives. Every manufacturer adds preservative to the food during processing. The purpose is generally to avoid spoilageduring the transportation time.

Because food is so important to survival, food preservation is one of the oldest technologies used by human beings. Different ways and means have been found and improved for the purpose. Boiling, freezing & refrigeration, pasteurizing, dehydrating, pickling are the traditional few. Sugar and salt are also often used as preservatives. Neuclear radiation is also being used now. Modified packaging techniques like vacuum packing and hypobaric packing also work as preservatives.

Chemical preservatives are also being used for quite some time now. They seem to be the best and the most effective for a longer shelf life and are generally fool proof for the preservation purpose.

Benzoates (such as sodium benzoate, benzoic acid) Nitrites (such as sodium nitrite) Sulphites (such as sulphur dioxide), Sorbates (such as sodium sorbate, potassium sorbate

All of these chemicals act as either antimicrobials or antioxidants or both. They either inhibit the activity of or kill the bacteria, molds, insects and other microorganisms. Antimicrobials, prevent the growth of molds, yeasts and bacteria and antioxidants keep foods from becoming rancid or developing black spots. They suppress the reaction when foods comes in contact with oxygen, heat, and some metals. They also prevent the loss of some essential amino acids some vitamins.

Some common preservatives and their primary activity

Chemical Affected	Organism(s)	Action	Use in Foods
Sulfites	Insects & Microorganisms	Antioxidant	Dried Fruits, Wine, Juice
Sodium Nitrite	Clostridia	Antimicrobial	Cured Meats
Propionic Acid	Molds	Antimicrobial	Bread, Cakes, Cheeses
Sorbic Acid	Molds	Antimicrobial	Cheeses, Cakes, Salad Dressing
Benzoic Acid	Yeasts & Molds	Antimicrobial	Soft Drinks, Ketchup, Salad Dressings

There are other antioxidants like Sodium Erythorbate, Erythorbic Acid, Sodium Diacetate, Sodium Succinate, Grape Seed Extract, Pine Bark Extract, Apple Extract Tea Proplyphenols, Succinic Acid and Ascorbic Acid and preservatives like Parabens and Sodium Dehydro Acetate used frequently for preservation.